Rotary valve arrangements have been proposed by many people. One recent example is that proposed by U.S. Pat. No. 5,526,780 (Wallis). Common to all these rotary valve arrangements is an opening in the rotary valve's periphery that periodically aligns with a similar shaped window in the combustion chamber. When the opening in the rotary valve's periphery aligns with the window in the combustion chamber, fluid can pass into (in case of the inlet stroke) and out of (in the case of the exhaust stroke) the combustion chamber. When the opening in the valve's periphery is not aligned with the window in the combustion chamber the contents of the cylinder are trapped during the compression and combustion stroke.
In most prior art arrangements the rotary valve is driven at a fixed angular velocity ratio to the crankshaft. This is achieved by way of mechanical drive mechanisms such as gear trains, chain drives or belt drives which transmit constant angular velocity ratios.
“Angular velocity ratio” is the ratio obtained when the angular velocity of the rotary valve is divided by the angular velocity of the crankshaft.
Although rotary valves for internal combustion (IC) engines are the subject of numerous patents none have been commercialized. This is a result of a myriad of problems characteristic to rotary valves that have never been adequately resolved. One particular arrangement that has resolved many of these problems is the rotary valve arrangement disclosed in U.S. Pat. No. 5,526,780. This arrangement consists of a single rotary valve per cylinder which incorporates both an inlet and exhaust port in the same valve. Whilst the mechanical problems afflicting this concept have been resolved other issues are now impacting on commercial adoption of this technology. In recent years increasingly stringent emissions regulations have been adopted around the world. The IC engine manufacturers are meeting these regulations by the production of IC engines with variable valve timing. In these engines the valve timing of the inlet and exhaust are independently varied.
The arrangement disclosed in U.S. Pat. No. 5,526,780 suffers from the problem that both the inlet and exhaust port are housed in the same valve thus making independent variation of the inlet and exhaust timing impossible. This is widely held to be such a disadvantage that it will prevent future commercialization of such rotary valves despite their other considerable advantages.
This invention addresses these problems with a mechanism that allows a rotary valve with both inlet and exhaust ports in the same valve to satisfactorily address these emission issues whilst also improving the IC engines efficiency. In addition this mechanism is also used to improve full throttle performance.
Valve timing is generally expressed as the location of the inlet open, inlet close, exhaust open and exhaust close points relative to the crankshaft position. The crankshaft position is generally specified as an angle relative to a reference location. This is generally chosen to be the location where the piston is at the top of its stroke (i.e. top dead centre—tdc). If the exhaust closes 15° after tdc the exhaust port will cease communication with the cylinder when the crankshaft has rotated 15° from the position where the piston was at tdc. In other instances the reference location is chosen to be the location where the piston is at the bottom of its stroke (i.e. bottom dead centre—bdc)
Alternatively valve timing can be thought of as a combination of durations—inlet duration, exhaust duration, close duration and overlap duration together with a initial position and phase. The initial position determines the relationship between the crankshaft position and the rotary valve position at some point.
“Overlap” is that portion of the engine cycle where both inlet and exhaust ports are both simultaneously open to the combustion chamber.
“Duration” is the angle the crankshaft rotates through between any two events.
“Inlet duration” is the angle the crankshaft rotates through when the inlet port is in communication with the combustion chamber i.e. between inlet open and inlet close. Similarly “exhaust duration” is the angle the crankshaft rotates through when the exhaust port is in communication with the combustion chamber i.e. between exhaust open and exhaust close. “Close duration” is the angle the crankshaft rotates through when neither the inlet nor the exhaust port are open to the combustion chamber i.e. between inlet close and exhaust open. This occurs during the compression and power strokes on a four-stroke engine. “Overlap duration” is the angle the crankshaft rotates through when both the inlet and exhaust ports are simultaneously open to the combustion chamber i.e. between inlet open and exhaust close.
In all internal combustion engines synchronization of the valve events to their correct position in the engine cycle is essential. Phase is used to describe this synchronization. If the phase is constant from cycle to cycle the valve events will occur in exactly the same position in the cycle from one cycle to the next.
The position in the cycle is defined by the crankshaft position. The position of the rotary valve is described by the angle the valve has rotated from a reference location usually chosen as one of the easily observable valve events—i.e. inlet valve open (ivo), inlet valve close (ivc), exhaust open (evo) or exhaust valve close (evc). For ease of reference we have chosen the reference location to be ivo. “Rotary valve position” is defined as the angle the valve has rotated from the ivo point.
For conventional rotary valve internal combustion engines using drive mechanisms that deliver constant angular velocity ratio, the position of the rotary valve relative to the cycle position can be represented by a graph of the type shown in FIG. 11. Line 53 defines the position of the rotary valve for all crankshaft positions. So long as the relationship defined by this line occurs on successive cycles, phase has remained constant. In the event the relationship between rotary valve position and crankshaft position is at some other time represented by line 54, a phase change is said to have occurred and its magnitude is σ. In the event line 53 is chosen as the reference, the phase is σ°.
“Phase” is defined as the distance in crankshaft degrees that the line 54 defining constant phase has shifted relative to a reference line 53 defining constant phase.
“Phase change” is defined as the distance in crankshaft degrees that any line defining constant phase has shifted relative to any other line defining constant phase.
Phase change is defined as positive if the change is such that the inlet valve opens later in the engine cycle. A phase change from line 53 to line 54 in FIG. 11 is positive.
Phase change is defined as negative if the change is such that the inlet valve opens earlier in the engine cycle.
In conventional poppet valve engines there are practical limitations as to how far the timing may be varied from its nominal position. This is a result of the fact that the poppet valves open into the combustion chamber. When the piston is at tdc on the induction stroke the crown of the piston is very close to the heads of the protruding poppet valves. The higher the compression ratio, the greater the number of valves and the greater the bore/stroke ratio the closer the valve must come to the piston crown. Modem engines seek to maximize these variables. Timing variations that require the poppet valve to protrude further into the combustion chamber are therefore restricted in magnitude. Compared to their full throttle timing, variations are generally restricted to opening the inlet later or closing the exhaust earlier, both of which increase the distance between the head of the poppet valve and the piston crown.
All engines require a certain amount of overlap at full throttle to obtain the optimum power result. At low throttle settings this overlap can result in excessive internal exhaust gas recirculation (EGR) causing poor combustion stability with resultant “rough running” and excessive hydrocarbon emissions. The poppet valve manufacturers vary the valve timing to reduce the overlap to a minimum at part throttle or low load operation. Generally speaking the timing variation is limited to the magnitude of the maximum angle the valve opens or closes from tdc. For example most engines typically require the inlet valve to open 15° before tdc and the exhaust valve to close 15° after tdc to obtain maximum power. Phase changes are typically limited to a maximum of about 15° from the full throttle phase position.
There is generally a practical limit to the amount of phase change that can be applied to a poppet valve arrangement with a fixed duration cam. If the inlet valve open position is moved from 15° before tdc to tdc when the engine is operating at low load, the inlet close point will also occur 15° later. This later valve closing will result in a considerable loss of charge that will be pumped out of the cylinder back into the inlet port with consequent loss of efficiency. Consequently phase changes are generally limited to a magnitude that will achieve a satisfactory internal EGR result—approximately 15°. In the event larger changes are required manufacturers have introduced devices that alter the inlet and exhaust duration. In this event the size of the allowable phase changes is extended.
Rotary valves on the other hand do not protrude into the combustion chamber. There is therefore no physical limit to how far the valve timing may be varied. This creates the possibility of solutions that are not available to poppet valve engines. This invention phases shifts a rotary valve with both inlet and exhaust ports in the same valve in response to changes in engine operating conditions. Essentially the inlet and exhaust are simultaneously phase changed an equal amount whilst maintaining their inlet and exhaust durations at their full throttle magnitude. This invention requires the use of large phase changes in certain operating situations. On a poppet valve engines such a strategy is not physically possible. For example if a poppet valve mechanism applied a simultaneous phase change of equal magnitude to both inlet and exhaust valves whilst maintaining the same full throttle inlet and exhaust durations, either the inlet or exhaust valves would soon hit the piston, depending on whether the phase change was positive or negative. On a poppet valve engines only small phase changes of this type can occur before the valves hit the piston. The magnitude of the phase change that can occur prior to the valves hitting the piston will vary with the design of the engine. However in modern high performance poppet valve IC engines (twin overhead cam 4 valve engines with high compression ratios) this would generally be limited to less than 10°.
Throughout this specification, in arrangements where the duration of inlet and/or exhaust is fixed, it is understood that a “large phase change” or a “large magnitude of phase change means a phase change greater than 15° and typically greater than 25°.
All known variable timing proposals for rotary valves have however adopted strategies that mimic those used by poppet valve engine manufacturers. All prior art variable timing rotary valve proposals use arrangements with separate valves for the intake and exhaust ports. These arrangements have the advantage that the inlet and exhaust port timing can be varied independently and can thus mimic the poppet valve strategy of independently phase changing the inlet and exhaust valve timing. U.S. Pat. No. 5,205,251 (Conklin) is an example.
U.S. Pat. No. 5,205,251 (Conklin) describes a means of varying the valve timing of a rotary valve engine fitted with two rotary valves per cylinder. One rotary valve contains an inlet port and the other rotary valve contains an exhaust port. The rotary valves are housed inside sleeves and are able to rotate within these sleeves. The sleeves are rotatably disposed within the cylinder head. Timing variation of the inlet or exhaust events is achieved by a combination of rotation of the sleeves and variation of the rotary valve's angular velocity during the cycle. In this arrangement the variation in the rotary valve's angular velocity during the cycle varies either the inlet and/or the exhaust duration. The rotation of the sleeve varies the location of the inlet and/or the exhaust events relative to the crankshaft or the phase of these events relative to the crankshaft. The combination of variations in the angular velocity of the rotary valves and rotation of the sleeves allows independent movement of the inlet open, inlet close, exhaust open, and exhaust close points.
The provision of a sleeve and an additional mechanism to vary its location is an additional complication and also introduces additional gas sealing difficulties. U.S. Pat. No. 5,205,251 remains silent on how gas sealing is achieved. However it is clear that gas sealing will be required between the combustion chamber and the sleeve and between the sleeve and the rotary valve. There is no known practical solution for this arrangement and the requirement to seal in two places merely increases the complexity.
The drive mechanism disclosed in U.S. Pat. No. 5,205,251 to vary the angular velocity of the rotary valve during the cycle is complicated and would be difficult to implement in practice. The eccentric gear must have provision to vary the eccentricity while it rotates and the idler that this gear engages must be able to move its centre continuously throughout the cycle. A separate mechanism is required for each valve.
Any arrangement that varies the timing by use of a sleeve requires a window in the cylinder head that is wider than the opening in the valve. This is well illustrated in FIGS. 2 and 5 in U.S. Pat. No. 5,205,251. As the breathing capacity of the rotary valve is determined in part by the width of the opening in the rotary valve, there is no practical requirement for the window in the head to be wider than the rotary valve opening apart from that introduced by the use of the sleeve. Consequently the breathing capacity of the rotary valve is unnecessarily limited. The wider window in the cylinder head also has the following additional problems. Firstly, the gas loads imposed on the rotary valve during combustion are directly proportional to the cylinder head window width and are therefore unnecessarily high in the case of applications using sleeves to vary timing. Secondly, the volume occupied by these windows is unnecessarily high and makes design of combustion chambers having the required compression ratios difficult.
A single rotary valve incorporating both inlet and exhaust ports in the same valve is a substantial improvement over arrangements requiring separate valves for the inlet and exhaust ports. The following considerations make this clear.
Two important features relevant to all valve mechanisms for internal combustion engines are the rate at which the valve opens and closes, and the maximum breathing capacity of the valve system. In the case of rotary valves the length of the window in the cylinder head and the valve diameter determine the rate at which the valve opens and closes. The length of the window is geometrically constrained by the requirement to have it located within the bore of the cylinder and can be made a similar length whether there are one or two valves per cylinder. The maximum breathing capacity is determined by the valve diameter. Thus, for the same maximum breathing capacity, the valve diameter for the rotary valve with a single inlet port must be the same as the valve diameter for a valve with both inlet and exhaust ports in the same valve. Consequently, a single valve incorporating both the inlet and exhaust ports in the same valve will have the same maximum breathing capacity and open and close rates (i.e. the same breathing capacity) as will two rotary valves incorporating inlet and exhaust ports in separate valves but with half the number of components.
In arrangements where maximum breathing capability is required it is necessary to make the diameter of the rotary valve as large as possible. Physical packaging constraints allow single rotary valves of much greater diameter than is possible with twin rotary valves. The ultimate breathing capacity of an arrangement with a single rotary valve incorporating inlet and exhaust ports in the same valve is therefore much greater than that of an arrangement with two rotary valves each of which contain a single port.
In addition, a twin rotary valve incorporating inlet and exhaust ports in separate valves will have twice the number of bearings and seals as required with a single valve incorporating both inlet and exhaust ports in the same valve.
Consequently, friction losses in the two-valve arrangement are potentially double those in the single valve arrangement with both inlet and exhaust ports in the same valve.
In the event other considerations require the use of two valves per cylinder, two rotary valves incorporating both inlet and exhaust ports in the same valve will have twice the opening and closing rate for the same window length as will two rotary valves of the same incorporating only a single port in each valve. This assumes the diameter of both types of valves is the same. In this case the arrangement with both inlet and exhaust ports in the same valve will have twice the maximum breathing capacity. Consequently two valves incorporating both inlet and exhaust ports in the same valve will have twice the breathing capacity of two valves of the same diameter incorporating the inlet and exhaust valves in separate rotary valves.
Whilst attempts have been made to address the issue of variable valve timing in rotary valve arrangements where the inlet port and exhaust port are accommodated in separate rotary valves, no attempts have been made to address the inherently more difficult arrangement where both the inlet and exhaust ports are accommodated in the same rotary valve.
This added difficulty arises because, in this arrangement, the phasing between the exhaust events and the inlet events are fixed by the geometry of the rotary valve. A simple phase change between a rotary valve incorporating both inlet and exhaust ports and the crankshaft cannot therefore effect a change in the location of the inlet and exhaust relative to each other. By way of comparison, the use of separate rotary valves for the inlet port and the exhaust port means a simple phase change between one or both of the rotary valves and the crankshaft will change the phasing between the inlet and exhaust and will alter the overlap.
In addition on a single rotary valve incorporating both inlet and exhaust ports in the same valve there is no known way of changing the overlap duration.
In a single rotary valve arrangement the overlap duration is physically determined by the width of the bridge between the inlet and exhaust ports on the rotary valve and the width of the window in the cylinder head. Typically the width of the bridge is smaller than the width of the window as shown in FIG. 6. This arrangement produces overlap. As the magnitude of the overlap is physically determined by the details machined into the rotary valve and cylinder head, there is no way of varying the magnitude of the overlap. Consequently, the conventional valve timing strategies used on poppet valves and twin rotary valves are not available to engines fitted with a single rotary valve. This is an inherent limitation of any rotary valve incorporating both inlet and exhaust ports in the same valve.
There are two instances in the patent literature where timing variation is mentioned in relation to rotary valves incorporating both inlet and exhaust ports in the same valve. GB patent 2 072 264 (Williams) describes a rotary valve engine incorporating both inlet and exhaust ports in the same valve. This single valve is connected to two or more cylinders. The arrangement as described is not capable of satisfactorily functioning as an IC engine. This can be ascertained by the following considerations. FIG. 5A of GB patent 2 072 264 and the text describe a rotary valve where the openings in the periphery of the rotary valve subtends an angle (centred on the rotational axis of the rotary valve) of 60°. The cylinder opening 101 communicating between the openings in the valve periphery and the cylinder subtend an angle of 45°. As the cylinder openings are 90° apart, the angle subtended between closing edge of one cylinder opening and the opening edge of the adjacent cylinder opening is 45°. It is clear that when the valve is rotated 45° clockwise from the position shown in FIG. 5 of GB patent 2 072 264 that the inlet port will be simultaneously open to both cylinder 50 and cylinder 52. As cylinder 52 is on the exhaust stroke and cylinder 50 is on the inlet stroke, the inlet port is now open to two cylinders on different strokes. This is clearly unworkable.
GB patent 2 072 264 seeks to make a virtue of this fact. It asserts that as a result of the angle subtended by the opening in the periphery of the valve being greater than the angle subtended by the cylinder opening it is possible to vary the length of time that the valve has full opening because of the mechanism that can vary the timing of the valve while the engine is running. The patent makes no disclosure as to how this variation in the length of time that the valve is fully open, is achieved. Further there is no known means of varying the timing to achieve such a result. The result cannot be achieved by introducing a phase change (the subject of this invention) as this will merely change the valve's timing but not the length of time the valve is fully open. The concept of varying the length of time the valve is fully opened has little merit in light of the following issue.
In any rotary valve engine the maximum breathing capacity is obtained by making the opening in the periphery of the valve and the window as large as possible. For any given duration the optimum breathing capacity is obtained when the width of the opening in the periphery of the valve and the width of the window are the same. When as disclosed in GB patent 2 072 264 the width of the window is deliberately made narrower than the width of the opening in the periphery, the maximum breathing capacity of the arrangement is reduced by virtue of the smaller window opening than would be available if both were the same size. The concept of then introducing some undisclosed method of increasing the time the valve is in the fully open condition (presumably to increase breathing capacity) has little merit given that it will never achieve the breathing capacity that a simple change to the geometry of the part will achieve.
These issues are all addressed in JP patent 9-32518 (Sakochi). In this patent a single rotary valve incorporating an inlet and exhaust port in the same valve is disclosed. This valve is shared between two cylinders. FIG. 11 of JP patent 9-32518 shows that the openings in the periphery of the valve and the window all have the same width and all subtend an angle of 45°. Further the angle subtended by the closing edge of one window and the opening edge of the adjacent window is also 45°. This overcomes the problem of GB patent 2 072 264 where the inlet (or exhaust) port can simultaneously be open to adjacent cylinders on different strokes. However this arrangement has a bridge between the inlet port and the exhaust port that subtends 45°. When this bridge is positioned directly over the window, the window is completely blocked. Hence this arrangement has zero overlap.
Zero overlap is a necessary restraint on any design where a single rotary valve feeds two or more adjacent cylinders.
Further the inlet (or exhaust) duration is 2 (A+B) where A is the angle subtended by the opening in the periphery of the valve and B is the angle subtended by the window. As both these angles are 45° in the case of JP patent 9-32518 the duration of the inlet or exhaust is restrained to be 180°.
Maximum inlet and exhaust duration of 180° is a necessary restraint on any design where a single rotary valve feeds two or more adjacent windows.
Both the zero overlap and maximum inlet and exhaust duration of 180° are formidable restraints on the design of any IC engine. While an engine with these restraints will work it will have a considerable maximum power disadvantage compared to modern IC engines which typically have 30° of overlap and 230° of duration.
A method of varying the phase between the valve and the crankshaft is also disclosed in JP patent 9-32518. This disclosure is for a device to make fine adjustments to the phase of the valve such that the valve can be maintained with the inlet port opening precisely at tdc on the induction stroke, and the exhaust opens precisely at bdc of the exhaust stroke. It is an adjustment mechanism to maintain the phase rather than a mechanism to vary the phase.
The essence of the present invention is the recognition that despite the fact a rotary valve incorporating both inlet and exhaust ports in the same valve, imposes considerable physical restraints on how the timing may be varied, other features unique to the rotary valve (in particular lack of valve protrusion into the combustion chamber) mean that advantages can be obtained by the use of an alternative strategy that makes use of these unique features. By dynamically changing the phase in response to the operating conditions of the engine improvements in load and emissions may be obtained. Further if changes in phase are combined with management of the throttle, smaller pumping losses will improve part throttle efficiency and improvements in NOx emissions will result.